Scilab Function
Last update : September 1997

dlgamma - derivative of gammaln function, psi function

### Calling Sequence

  `y = dlgamma(x)`

### Parameters

- `x`: real vector
- `y`: real vector with same size.

### Description

`dlgamma(x)` evaluates, at all the elements of `x` the logarithmic derivative of the gamma function which corresponds also to the derivative of the gammaln function :

             d/dx (gamma(x)) / gamma(x) = d/dx (ln gamma(x))

`x` must be real. Also known as the psi function.

### Examples

    dlgamma(0.5)

### See Also

`gamma`, `gammaln`,

### Author

W. J. Cody (code from Netlib (specfun))